/**
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 * 
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *  
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 */
package org.cspoker.ai.experiments.util;
//--------------------------------------
//Systematically generate combinations.
//--------------------------------------

import java.math.BigInteger;
/**
 * The source code is free for you to use in whatever way you wish.
 * http://www.merriampark.com/comb.htm
 */
public class CombinationGenerator {

private int[] a;
private int n;
private int r;
private BigInteger numLeft;
private BigInteger total;

//------------
// Constructor
//------------

public CombinationGenerator (int n, int r) {
 if (r > n) {
   throw new IllegalArgumentException ();
 }
 if (n < 1) {
   throw new IllegalArgumentException ();
 }
 this.n = n;
 this.r = r;
 a = new int[r];
 BigInteger nFact = getFactorial (n);
 BigInteger rFact = getFactorial (r);
 BigInteger nminusrFact = getFactorial (n - r);
 total = nFact.divide (rFact.multiply (nminusrFact));
 reset ();
}

//------
// Reset
//------

public void reset () {
 for (int i = 0; i < a.length; i++) {
   a[i] = i;
 }
 numLeft = new BigInteger (total.toString ());
}

//------------------------------------------------
// Return number of combinations not yet generated
//------------------------------------------------

public BigInteger getNumLeft () {
 return numLeft;
}

//-----------------------------
// Are there more combinations?
//-----------------------------

public boolean hasMore () {
 return numLeft.compareTo (BigInteger.ZERO) == 1;
}

//------------------------------------
// Return total number of combinations
//------------------------------------

public BigInteger getTotal () {
 return total;
}

//------------------
// Compute factorial
//------------------

private static BigInteger getFactorial (int n) {
 BigInteger fact = BigInteger.ONE;
 for (int i = n; i > 1; i--) {
   fact = fact.multiply (new BigInteger (Integer.toString (i)));
 }
 return fact;
}

//--------------------------------------------------------
// Generate next combination (algorithm from Rosen p. 286)
//--------------------------------------------------------

public int[] getNext () {

 if (numLeft.equals (total)) {
   numLeft = numLeft.subtract (BigInteger.ONE);
   return a;
 }

 int i = r - 1;
 while (a[i] == n - r + i) {
   i--;
 }
 a[i] = a[i] + 1;
 for (int j = i + 1; j < r; j++) {
   a[j] = a[i] + j - i;
 }

 numLeft = numLeft.subtract (BigInteger.ONE);
 return a;

}
}

